The following paragraphs contain some discussion, which is illuminated by the innovations disclosed in this application, and any discussion of actual or proposed or possible approaches in this Background section does not imply that those approaches are prior art.
Natural resources such as oil or gas residing in a subterranean formation can be recovered via the formation of wells that penetrate the formation. In particular, a wellbore is typically drilled down to the formation while circulating a drilling fluid (also known as a drilling mud) through the wellbore. During the drilling process, the drill bit generates drill cuttings that consist of small pieces of shale and rock. The drilling fluid carries the drill cuttings in a return flow stream back to the well drilling platform. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run into the wellbore. The drilling fluid is then usually circulated downwardly through the interior of the pipe and upwardly through the annulus, which is located between the exterior of the pipe and the walls of the well bore.
Primary cementing is then usually performed whereby a cement slurry is pumped down through the string of pipe and into the annulus between the string of pipe and the walls of the wellbore to allow the cement slurry to set into an impermeable cement column and thereby seal the annulus. Subsequent secondary cementing operations, i.e., cementing operations occurring after the primary cementing operation, may also be performed. One example of a secondary cementing operation is squeeze cementing whereby a cement slurry is forced under pressure to areas of lost integrity in the annulus to seal off those areas.
Unfortunately, the fluids used in such downhole operations may be lost to the subterranean formation while circulating the fluids in the wellbore. In particular, the fluids may enter the subterranean formation via depleted zones, zones of relatively low pressure, naturally occurring fractures, weak zones having fracture gradients exceeded by the hydrostatic pressure of the drilling fluid, and so forth. As a result, the services provided by the fluids are more difficult to achieve. For example, a problem known as lost circulation may occur in which the circulation of the drilling fluid in the wellbore drops due to it being lost to the formation. Its circulation may eventually become too low to allow for further drilling of the wellbore. Also, a cement slurry may be lost to the formation as it is being placed in the annulus, thereby rendering it ineffective in isolating the adjacent subterranean formation. In particular, the amount of cement slurry may be insufficient to fill the annulus from top to bottom during primary cementing or to fill areas of lost integrity in a pre-existing cement column during secondary cementing. Further, dehydration of the cement slurry may result, compromising the strength of the cement that forms in the annulus.
Traditional methods of overcoming the problems described above include sealing the zones through which the fluids can enter the subterranean formation with thixotropic cements, non-aqueous dispersions of clays, sodium silicate solutions in combination with calcium salt sweeps, and fluids containing inert platelets such as mica. However, the presence of such sealants in the formation may block the flow of oil or gas into the wellbore when it is desirable to begin production. Further, those materials may contaminate fresh water produced by the formation ahead of the oil or gas. Unfortunately, the sealants typically cannot be easily removed from the formation before production. A need therefore exists to develop a way to prevent the loss of fluid to the subterranean formation without adversely affecting the production of water, oil, or gas by the formation.